The current trend for the cellular technology is cellular phones that can be used in areas of different wireless communication standards. As an example, there are four Global System for Mobile communications (GSM) bands in use around the world. Two of these GSM bands, GSM 850 and GSM 1900, are used almost exclusively in North America, while the other two bands, GSM 800 and GSM 1800, are widely used in other parts of the world. The numbers after “GSM” refer to the center frequency in megahertz (MHz). Since there are four GSM bands, cellular phone components such as switch modules and power amplifiers have been developed to support some or all of the available GSM bands.
A prior art switch module of interest includes two bi-directional signal paths to both receive and transmit signals on each of the bi-directional signal paths. The first bi-directional signal path is used to receive and transmit signals in the GSM 1800 and GSM 1900 bands, while the second bi-directional signal path is used to receive and transmit signal in the GSM 850 and GSM 900 bands. Each bi-directional signal path is connected to an exclusive receive signal path and an exclusive transmit signal path. The switch module utilizes high and low pass filters to direct incoming signals to the proper bi-directional signal paths. Furthermore, since GSM cellular phones are half-duplex cellular phones, the switch module utilizes diodes to isolate the receive path from the corresponding transmit signal path to switch between receiving and transmitting modes. The use of diodes is superior to the use of transistors with respect insertion loss for simple switches such as above.
A prior art power amplifier module of interest that can be used with the above-described prior art switch module includes two signal paths that connect to the corresponding transmit signal paths of the switch module. On each of these two signal paths of the power amplifier module, an amplifier, an output matching network and a capacitor are connected in series. The amplifier provides amplified signals for transmission. The output matching network transforms the impedance of the amplifier from it's native impedance (e.g., 1 or 2 Ohms) to the required impedance of the antenna (e.g., 50 Ohms). The capacitor blocks current from being conducted to downstream circuits in the switching module so that the downstream circuits are not biased inadvertently.
Similar to other electronic components for handheld devices, there is a continuing need for smaller cellular phone components, such as switching modules and power amplifier modules. This continuing need is driven by the desire of consumers for compact cellular phones, as well as cellular phones with increased functionalities, such as color screens, digital cameras and/or Global Positioning Systems (GPS). These functionalities require additional space, which necessitates even smaller traditional cellular phone components to produce the compact cellular phones. In addition to space, each of these functionalities places a demand on the cellular phone battery, which reduces the overall operable life of a cellular phone. Therefore, the traditional cellular phone components such as switching modules and power amplifier modules need to be small in size and power efficient.